Configure BGP for beginners !

Configure BGP for beginners !

Dear Valued Reader,
Good morning ! Good afternoon ! Good evening

Today I'm going to assist you to configure BGP.

Scenario !


Here I have four routers named R1, R2-R3, and R4 which are belongs to AS-1, AS-23, and AS-4 respectively.

Here I'm going to configure EBGP (External Border Gateway Protocol) between R1-R2 and R3-R4. As we know we configured EBGP in those routers which is responsible to connect between different Autonomous System.

I'm going to configure IBGP (Internal Border Gateway Protocol) between R2 and R3. As we know we configured IBGP in those AS routers which Autonomous System is working as a transit AS. Here Autonomous System 23 is called as transit Autonomous System because it is responsible to connect different AS.

Ip address are configured as below :

on router R1
R1#show ip interface brief
Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0            192.168.12.1    YES manual up                    up     
FastEthernet0/1            unassigned      YES unset  administratively down down   
Loopback1                  1.1.1.1         YES manual up                    up

on router R2
R2#show ip interface brief
Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0            192.168.23.2    YES manual up                    up     
FastEthernet0/1            192.168.12.2    YES manual up                    up     
Loopback2                  2.2.2.2         YES manual up                    up

on router R3
R3#show ip interface brief 
Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0            192.168.23.3    YES manual up                    up     
FastEthernet0/1            192.168.34.3    YES manual up                    up     
Loopback3                  3.3.3.3         YES manual up                    up

on router R4
R4#show ip interface brief
Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0            192.168.34.4    YES manual up                    up     
FastEthernet0/1            unassigned      YES unset  administratively down down   
Loopback4                  4.4.4.4         YES manual up                    up

BGP are configured as below
on R1
R1#show running-config | begin bgp
router bgp 1
 no synchronization
 bgp log-neighbor-changes
 network 1.1.1.0 mask 255.255.255.0
 neighbor 192.168.12.2 remote-as 23
 no auto-summary

on R2
R2#show running-config | begin bgp
router bgp 23
 no synchronization
 bgp log-neighbor-changes
 network 192.168.12.0 mask 255.255.255.252
 neighbor 3.3.3.3 remote-as 23
 neighbor 3.3.3.3 update-source Loopback2
 neighbor 3.3.3.3 next-hop-self
 neighbor 192.168.12.1 remote-as 1
 no auto-summary

on R3
R3#show running-config | begin bgp
router bgp 23
 no synchronization
 bgp log-neighbor-changes
 network 192.168.34.0
 neighbor 2.2.2.2 remote-as 23
 neighbor 2.2.2.2 update-source Loopback3
 neighbor 2.2.2.2 next-hop-self
 neighbor 192.168.34.4 remote-as 4
 no auto-summary

on R4
R4#show running-config | begin bgp
router bgp 4
 no synchronization
 bgp log-neighbor-changes
 network 4.4.4.0 mask 255.255.255.0
 neighbor 192.168.34.3 remote-as 23
 no auto-summary

We have configued IGP on AS-23 as below

on R2
R2#show running-config | begin ospf
router ospf 23
 log-adjacency-changes
 network 2.2.2.0 0.0.0.255 area 0
 network 192.168.23.0 0.0.0.255 area 0

on R3
R3#show running-config | begin ospf
router ospf 23
 log-adjacency-changes
 network 3.3.3.0 0.0.0.255 area 0
 network 192.168.23.0 0.0.0.255 area 0

If you have any questions regarding why we put particular command on particular internface please don't feel hesitate to ask me.

Thank you.

cheers !

Keep smile ! Keep geek (y)

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